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U.S. Rep. Jesse Jackson Jr. is responding well to treatment for bipolar depression, the Mayo Clinic said Monday.

The Rochester, Minn.-based clinic said Jackson is regaining his strength but offered no further information on his condition.

In early July, the congressman's office announced he was "receiving intensive medical treatment at a residential treatment facility for a mood disorder." A few weeks later, his office said he was undergoing an "extensive inpatient evaluation for depression and gastrointestinal issues" at the Mayo Clinic.

Jackson's wife, Sandi, said earlier this month her husband had "good days and bad days" and doctors were increasing his depression medication to "therapeutic levels."

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The Illinois Democrat and son of the Rev. Jesse Jackson, the civil rights leader, has not been on Capitol Hill since late May.

Jackson and his family have not said much about his ordeal, though his father told The Huffington Post that when he visited his son in Washington in June, he learned the junior Jackson hadn't slept in three days.

What the family thought was exhaustion, the Rev. Jackson said, was "something much deeper, much broader, and it lasted much longer."

Sandi Jackson has firmly denied her husband had attempted suicide or was receiving help for alcohol or drug addiction.

She said earlier this month it was unclear when he might return to work -- including whether he would be at the Democratic National Convention in early September.

Jackson's illness comes as the House Ethics Committee is examining allegations that in 2008, he or one of his associates offered to raise money for then-Illinois Gov. Rod Blagojevich in exchange for Jackson being appointed to the Senate seat vacated by Barack Obama after he was elected president.

The congressman has maintained his innocence and pledged to continue to cooperate with authorities.

Blagojevich was convicted last year on corruption charges in connection with his efforts to profit from appointing the successor to the Senate seat. He began serving a 14-year sentence in March.

Bipolar disorder is a treatable condition that affects parts of the brain controlling emotion, thought and drive, the Mayo Clinic says. Many Americans suffer from it, and it is most likely caused by a complex set of genetic and environmental factors, it says.

Medical experts are still weighing whether gastric bypass surgery that Jackson underwent in 2004 for weight loss might have helped trigger his depression, his wife said. The Mayo Clinic said that type of surgery is increasingly common in the United States and can change how the body absorbs food, vitamins, nutrients and medications.